MC68HC05X16 Datasheet, PDF (37/232 Pages) Freescale Semiconductor, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

Freescale Semiconductor, Inc.
2.3.11 SCLK
The SCLK pin is the clock output pin of the SCI transmitter.
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2.3.12 OSC1, OSC2
These pins provide control input for an on-chip oscillator circuit. A crystal, ceramic resonator or
external clock signal connected to these pins supplies the oscillator clock. The oscillator frequency
(f_OSC) is divided by two, four, eight or ten to give the internal bus frequency (f_OP). There is also a
software option which introduces an additional divide by 16 into the oscillator clock, giving an
internal bus frequency of f_OSC/32, /64, /128 or /160.
2.3.12.1 Crystal
The circuit shown in Figure 2-6(a) is recommended when using either a crystal or a ceramic
resonator. An internal feedback resistor is provided on-chip between OSC1 and OSC2.
Figure 2-6(d) lists the recommended capacitance values. The internal oscillator is designed to
interface with an AT-cut parallel-resonant quartz crystal resonator in the frequency range specified
for f_OSC (see Section 12.4). Use of an external CMOS oscillator is recommended when crystals
outside the specified ranges are to be used. The crystal and associated components should be
mounted as close as possible to the input pins to minimise output distortion and start-up
stabilization time. The manufacturer of the particular crystal being considered should be consulted
for specific information.
2.3.12.2 Ceramic resonator
A ceramic resonator may be used instead of a crystal in cost sensitive applications for frequencies up
to 8MHz external. The circuit shown in Figure 2-6(a) is recommended when using either a crystal or a
ceramic resonator. Figure 2-6(d) lists the recommended capacitance and feedback resistance values.
The manufacturer of the particular ceramic resonator being considered should be consulted for specific
information. This option is recommended only for applications that operate at an external clock
frequency of 8MHz or less. Any application requiring an external operating frequency greater that
8MHz should use either a crystal oscillator or an external CMOS compatible clock source.
2.3.12.3 External clock
When using an external clock the OSC1 and OSC2 pins should be driven in antiphase, as shown
in Figure 2-6(c). The t_OXOV or t_ILCH specifications (see Section 12.4) do not apply when using an
external clock input. The equivalent specification of the external clock source should be used in
lieu of t_OXOV or t_ILCH.
MC68HC05X16 MODES OF OPERATION AND PIN DESCRIPTIONS
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